(i) Field of the Invention
The present invention relates to an image display unit using a crossflow image transfer system, which transfers a toner image on an image transfer belt and displays the image transferred thereon.
(ii) Description of the Prior Art
Recently, an image formation unit using an electrophotographic system, which is so excellent in resolution as to enable providing a clear image, have been remarkably improved in its performance, as represented by a laser printer. Further, as a practical application of the image formation unit, an image display unit for a guide bulletin board or poster display board also has been popularized.
Hereinafter, such an image display unit is explained.
FIG. 14 is a schematic side view illustrating an conventional image display unit, and FIG. 15 is a perspective view showing the image transferring steps in the conventional image display unit. FIG. 16 is a perspective view representing a state of a displayed image in the conventional display unit, and FIG. 17 is a typical schematic view illustrating a formation of a toner layer on an image developing roller in the conventional image formation unit.
In FIGS. 14 to 16, the constitution of the image display unit is generally separated into a toner image formation unit 1 and a transfer belt 2 serving as a display board.
The toner image formation unit 1 comprises a toner image carrier 3 of a photosensitive material drum whose surface is coated with a layer of an organic photo-conductive material and devices for forming a toner image on the toner image carrier 3. The items of the devices are a charging means 4, developing means 5, cleaning means 6 and discharging means 7, etc. each of which is positioned around the toner image carrier 3, and an exposing means 8 for radiating a laser beam which is disposed under the toner image carrier 3. The toner image carrier 3 is rotated counterclockwise so that the image thereon is continuously formed on the transfer belt 2, and the transfer belt 2 displays the complete image on one of its own surfaces opposite to the toner image formation unit 1 to thereby serve as a so-called display means.
A successive flow of the image formation steps is explained below.
In FIGS. 14 to 16, the charging means 4 charges uniformly the surface of the toner image carrier 3 passed by to around minus 600 V. The exposing means 8 formed of optical system devices such as a laser radiator, polygon mirror, etc. radiates a laser beam based upon a supplied image signal thereto and thereby raises a surface voltage of the exposed portion in the toner image carrier 3 to around minus 100 V to provide resultingly the surface of the toner image carrier 3 with an electrostatic latent image. The developing means 5 forms the toner image on the toner image carrier 3 so as to change the electrostatic latent image into a visible image, by pushing a developing roller 10 to which a negatively charged toner 9 has adhered against the toner image carrier 3 and thus transferring the toner 9 to the electrostatic latent image on the surface of the toner image carrier 3. As illustrated in FIG. 17, the width of a monochromatic toner layer 11 such as a black layer etc. is prevented from extending beyond the width of the toner image carrier 3 by sealing both the side ends of the width of the layer 11 with sealing members 11. A transferring means 14 applies a positive voltage to the transfer belt 2 from the back thereof in order to transfer the toner image on the surface of the toner image carrier 3 onto the transfer belt 2 to thereby pull and separate the negatively charged toner image from the surface of the toner image carrier 3, and resultingly transfers continuously the toner image to the transfer belt 2.
After the transfer onto the transfer belt 2 is completed, the cleaning means 6 removes and recovers residual toner on the surface of the toner image carrier 3 by means of a cleaning blade or cleaning brush to thus clean the surface of the toner image carrier 3 physically. The recovered toner is conveyed toward the developing means 5 by a toner conveying means 15 (as denoted by an arrow of the dotted line in FIG. 14) and reclaimed as a toner material. Since the transfer efficiency of the toner image carrier 3 onto the transfer belt 2 is around 90 to 95% only at present, the toner material is utilized effectively by recovering and reclaiming all of the residual toner on the toner image carrier 3. The discharging means 7 neutralizes a negative charge remaining after removal of the residual toner on the surface of the toner image carrier 3 and thus cleans the surface thereof electrically.
After the image transfer is conducted, as shown by FIG. 16, the surface of the transfer belt 2, having the transferred image thereon, is moved to the position opposite to the toner image formation unit 1 and the complete image is displayed there. The transfer belt 2 is made of non-photosensitive material and corresponds to an intermediate transfer means in a present image formation device applied to a color display unit. In other words an image formation unit is defined as a unit to finally fix an image to a print paper, and an image display unit is defined as a unit to display an image and subsequently erase the image when the display ends.
When it is ended to display the image on the transfer belt 2, there the entirety of the image is erased on the transfer belt 2 (the image can be taken as a residual toner material just when the display is over) so as to prepare for the following image transfer. For this purpose, the whole of the image on the transfer belt 2 (it remains as an aggregation of the toner 9 itself because it is neither heated nor fixed) is removed and recovered by means of a cleaning blade or cleaning brush of the cleaning means 16 used exclusively for the transfer belt 2 to thus clean the surface of the toner image carrier 3. The recovered toner is conveyed toward the developing means 5 by a toner conveying means 17 (as denoted by an arrow of the dotted line in FIG. 14) and supplemented (reclaimed) as a toner material.
As mentioned above, a successive flow of the image formation steps is completed. However, in such a conventional image display unit, a rotational direction of the toner image carrier 3 is parallel to that of the transfer belt 2 and consequentially it is required that the width of the toner image carrier 3 matches with that of the transfer belt 2. Accordingly, even in the image display unit for handling a monochrome system as described above, the developing means 5 and the exposing means 8 each occupy a large space correspondingly to the widths of the toner image carrier 3 and the transfer belt 2. Especially, when there is produced a toner image formation unit designed for a colored image, a developing means is necessary for each of the four primary colors of cyan, magenta, yellow and black, and even as far as this concerned, the number of the parts increases up to four times as many as that of a monochrome system. Further, the toner image carrier is necessarily changed from the photosensitive material drum to a photosensitive material belt in order an exposing means is shared by each developing means for the four colors, accordingly the number and the sizes of the parts are inevitably increased so largely. For the above reasons, there is a problem that it is difficult to miniaturize an image display unit and reduce the number of the parts.